In a conventional etching technique using gas plasma, observing the state of a sample to be etched by some way is known. As the conventional etching technique, for example, Japanese patent application laid-open No.1-183124 (1989) discloses an etching method that, in a process of forming a trench in a treated material, prior to conducting the plasma etching, an oxide film for detecting the end point of etching on the treated material is formed and then a polysilicon film equal to the depth of trench is formed thereon, thereafter removing the oxide film and polysilicon film to open the trench. A product by the reaction of the oxide film and ion gas plasma is detected by emission spectrum analysis in the process of conducting the plasma etching.
Also, Japanese patent application laid-open No.1-278728 (1989) discloses an etching method that, in forming a trench in a treated material, prior to conducting the plasma etching, predetermined ions are ion-implanted up to a position equal to the depth of the trench to be measured from the upper surface at a position to form the trench in the treated material, and a product formed by the ions is detected by emission spectrum analysis or mass spectrum analysis in the process of conducting the plasma etching.
When plasma etching, further to the detection of the end point of etching being solved by Japanese patent application laid-open Nos.1-183124 (1989) and 1-278728 (1989), "a method for conducting the etching" that does not generate any etch residue or etch stop is also important.
Also, it is desired that the taper angle of a trench to be formed by etching be constant regardless of the etch area.
Further, a problem in the plasma etching is that it can easily performed according to a variation in the ratio (i.e., a specification required to etching) of etch area to an etched sample.
Also, the above problems need to be solved, with succeeding the conventional plasma etching technique, i.e., by means to be within the range of conventional facilities.
However, means to solve the above problems need to have such a property that can be performed even by introducing additionally a larger-scale automatic control unit as the case may be, i.e., expandability to be prepared to the prospects for the future.